1. Field of the Invention
The present invention relates to a system for notifying a person of a level of danger of an occurrence of tire failure, which assesses and notifies a driver of a level of danger of an occurrence of failure of a tire mounted to an automobile or other such vehicle.
2. Description of the Related Art
Today, as vehicles become faster, a tire mounted to a vehicle needs to function at high speed with safety. Thus, there have been great improvements made in the durability of mounted tires, and particularly in the durability while running at high speed. Accordingly, at present, there is almost no problem of failing, bursting or the like of the mounted tire when it runs normally.
However, in cases where the mounted tire is used when tire inflation pressure has dropped drastically, or where the vehicle runs for a long time at an extremely high speed, or where a heavy load is provided to the mounted tire, there is an increased probability of the tire tread members breaking away from the tire main body, or of an end portion of a tire belt layer that is comprised of a steel belt separating from the tire main body. In other words, there is an increase in the level of danger of an occurrence of failure of the mounted tire. Further, when such conditions continue, there is an increase in the danger of the mounted tire finally failing and bursting.
Thus, a variety of proposals have been made for an air pressure warning system which constantly manages the tire inflation pressure, and notifies the driver of the drop in the tire inflation pressure when the air pressure of the tire becomes below a given level.
The above-mentioned air pressure warning system constantly monitors the tire inflation pressure, and the system is effective for a case where the tire inflation pressure drops extremely due to a certain cause, or for a case where the tire is punctured and the tire inflation pressure drops gradually, for example. However, in a case where the tire is used under a condition in which tire usage conditions are complicatedly overlapped, such as a case where the tire inflation pressure is relatively low and a relatively heavy load is provided to the mounted tire as the vehicle runs for a relatively long duration of time at high speed, simple constant monitoring of the tire inflation pressure does not work to predict and to notify the driver that the danger level of the mounted tire failure has become great before the failure occurs. Once the failure has occurred, even if the air pressure warning system provides a warning based on the drop in the tire inflation pressure, there is a fear that the vehicle will lose control of its movement and will crash.
The present invention has been made in view of solving the above-mentioned problems in the conventional art, and an object of the present invention is therefore to provide a system for notifying a person of a level of danger of an occurrence of tire failure, capable of notifying and also warning the driver of a high level of the danger of the occurrence of the tire failure before the tire failure occurs, even in a case where a tire that is mounted to an automobile or other such vehicle is used under a variety of overlapped conditions.
The invention provides a system for assessing a level of danger of an occurrence of failure of a mounted tire to a vehicle, and notifying a person of the level of the danger according to a result of the assessment, the system comprising: a tire inflation pressure measuring device for monitoring a tire inflation pressure of the mounted tire; a tire running speed measuring device for monitoring a tire running speed of the mounted tire; a danger level assessment device for, at least in a case where the tire running speed obtained by the monitoring is higher than a given reference speed, calculating a danger level assessment value indicating an index showing a probability of the occurrence of the failure of the mounted tire from the tire inflation pressure obtained by the monitoring by the tire inflation pressure measuring device and from the tire running speed obtained by the monitoring by the tire running speed measuring device, based on a danger level assessing function, and assessing the danger level of the occurrence of the tire failure of the mounted tire from the danger level assessment value; and a notification device for notifying a person of the danger level of the occurrence of the failure of the mounted tire, according to a result of the assessment of the danger level, wherein the danger level assessing function is a function of the tire running speed and of the tire inflation pressure, in which, at least when the tire running speed is in a speed range above the given reference speed, a value of the function monotonously increases as the tire running speed increases, and the value of the function increases as the tire inflation pressure decreases.
It is preferable that the danger level assessing function has a first linear function defined in a speed range equal to or below the reference speed in which a value of the function remains fixed regardless of increase in the tire running speed, or increases linearly with the tire running speed, and a second linear function defined in a speed range above the reference speed in which a value of the function increases linearly with the tire running speed; and wherein the first linear function and the second linear function connect at the reference speed and a gradient of the second linear function with respect to the tire running speed is greater than a gradient of the first linear function with respect to the tire running speed.
More preferably, the gradient of the first linear function and the gradient of the second linear function are determined by the tire inflation pressure.
Still more preferably, the gradient of the first linear function is equal to or above 0, and is equal to or less than 0.02 times a calculated value produced from the first linear function at a tire running speed 0 under a condition of a tire inflation pressure to be set of the mounted tire; and the gradient of the second linear function is greater than 0.02 times, and equal to or less than 1.0 times, the calculated value produced from the first linear function at the tire running speed 0 under the condition.
It is also preferable that the danger level assessment device adds a cumulative value determined according to a usage history of the mounted tire to a calculated value produced from the danger level assessing function, whereby the danger level assessment value is calculated.
More preferably, the danger level assessment device multiplies a duration of time for which the mounted tire is used by a function assessment reference value calculated value from the danger level assessing function at a tire running speed that is produced by multiplying the reference speed by the given value greater than 1, whereby the cumulative value is obtained.
Alternatively, the danger level assessment device preferably multiplies a sum of calculated values in a past for the mounted tire from the danger level assessing function by a function assessment reference value calculated from the danger level assessing function at a tire running speed that is produced by multiplying the reference speed by the given value greater than 1, whereby the cumulative value is obtained.
Alternatively the danger level assessment device more preferably calculates a weighted average between: a value produced by multiplying a product of a duration of time for which the mounted tire is used and a function assessment reference value calculated from the danger level assessing function at a tire running speed that is produced by multiplying the reference speed by a given value greater than 1, by a given number of times; and a value produced by multiplying a product of a sum of calculated values in a past for the mounted tire from the danger level assessing function and the function assessment reference value by a given number of times, whereby the cumulative value is obtained.
It is also preferable that the danger level assessing function with respect to the tire running speed when the tire inflation pressure is at a fixed level is a function obtained by approximating a characteristic function of a rolling resistance value that indicates a dependency of the mounted tire""s rolling resistance on the tire running speed using two straight-line or curved-line functions which are connected to each other at the reference speed, and multiplying each of these straight-line or curved-line functions by a given coefficient; and a value of the coefficient used in the speed range above the reference speed is a value equivalent to or greater than a value of the coefficient used in the speed range that is equal to or below the reference speed.
It is still also preferable that sensitivity coefficients which indicate gradients of the danger level assessing function with respect to the tire running speed, and which include a first sensitivity coefficient for the speed range equal to or below the reference speed and a second sensitivity coefficient for the speed range above the reference speed, decrease linearly as the tire inflation pressure increases.
The system, preferably further comprises a load measuring device for monitoring a tire load while the vehicle runs, wherein the danger level assessment device calculates a tire load ratio based on a load obtained from the load measuring device by the monitoring, and adjusts a calculated value produced from the danger level assessing function based on the tire load ratio.